The present invention relates to a hydraulic pump comprising at least one reciprocating piston sliding in a stationary cylinder, this pump comprising, furthermore, a non-return suction valve arranged between a source of fluid under low pressure and a working chamber defined in the cylinder, and a first non-return delivery valve arranged between the working chamber and an outlet chamber for the fluid under high pressure.
Such a pump is commonly used in hydraulic brake circuits comprising particularly a wheel anti-lock system.
U.S. Pat. No. 4,883,327 describes, for example, such a pump in a use as mentioned above. The main disadvantage of pumps of this type is that they generate noise and vibrations essentially at the moment when the pump begins to deliver.
It has been found that the levels of noise and of vibrations largely depend on the filling of the working chamber of the pump and on the pressure prevailing in the outlet chamber of the pump at the start of delivery.
It is known from DE-C-115 392 a double acting pump the power of which is limited by a communication between one of the working chambers in delivery period and the other working chamber in suction period from a given stroke of the piston at both sides of a middle point. This pump does not provide a cramming of a working chamber.